cladistic

Bernard Baum wrote:
> There is an opinion, supported by a great number of people, that
distance
> method are not really cladistic methods. I disagree, besides the
> semantic aspect of it. What is your position on this and what are your
> reasons for your position.
and Joe Felsenstein replied:
> If "cladistic" refers to a position on classification, it has a distinct
> meaning (make only monophyletic groups -- "holophyletic" in Ashlock's
> terminology). But the decision to use distance methods, as opposed to
> parsimony (or other approaches) does not say anything
> about how one takes the resulting phylogenies and makes them into
> classifications. So in the sense of classification, they are neither
> "cladistic" nor "phenetic" nor "evolutionary systematic".
>> The other meaning of "cladistic" refers to methods for inferring
> phylogenies. There it means "a method approved of by J. S. Farris".
> By this definition, distance methods are not cladistic.
>> Some people think "cladistic" in phylogenies means using the essential
> information and not obscuring it with noise. In that sense no method
> is cladistic, or else they all are.
I agree with Joe's characterization of cladistic classification
but in terms of inferring phylogenies, cladistic methods have
generally been associated with the parsimony method and, while
this method can be applied more broadly to other procedures as
well, there is justification for tracing an important aspect of
commonly encountered parsimony methods to the "father" of
cladistic inference methods, Willi Hennig.
One of Hennig's primary contributions to systematics was his
distinction between types of similarity. He advocated that it is
inappropriate to use symplesiomorphic (shared primitive)
similarities as supporting evidence for the monophyly (or
holophyly) of a clade. Only synapomorphic (shared evolutionary
novelties relative to one or more outgroups) features should
be used. In this sense, distance methods are not cladistic
because they confound plesiomorphic and apomorphic similarities.
Cladistic methods also emphasize the analysis of character
congruence. Methods that generate a composite distance value
between taxa (sequences) do not allow for such an analysis
because they cannot be related back to specific attributes
(characters) of an organism.
Doug Eernisse
Museum of Zoology
Univ. of Michigan